The present invention relates generally to printing and package decoration and, more particularly, to an apparatus for measuring the ink, photographic emulsion, or other opaque medium coverage of a translucent sheet of material which has been provided with opaque artwork identical to that which is to be printed, in a particular color, on package material in a mass-production package printing operation.
In the high-speed production of packaging material, each color which is printed on a package is, in most cases, printed by a separate ink or dye on a separate printing roll or press. In order to determine the amount of ink that will be required for any particular packaging project, it is customary for the manufacture of the product which is to be packaged to furnish the package producer with separate transparencies having opaque portions corresponding to the artwork for each color to be printed, i.e. if three separate colors are to be printed on a package, the manufacturer would furnish the package producer with three separate transparencies, each showing the pring configuration for a particular color. The package producer computes the total area coverage for each separate color from the transparencies as a step in determining the total amount of ink of each color which will be required for the particular project. The task of determining the area coverage of a transparent sheet of material with opaque medium may be relatively simple, as when the artwork for a particular color consists of a few regular geometric shapes of constant density or intensity. However, when artwork consists of irregular shapes, such as alpha-numeric printing or the like, or of varying densities, the task of accurate area coverage estimation may range from quite time-consuming to nearly impossible. The conventional method for computing area coverage for irregular opaque shapes is to break the shapes down into a number of small, substantially regular figures, such as rectangles and triangles, and to then take the sum of the areas of these small regular figures. Due to the large number of computations and approximations that must be made using this method, it is not uncommon for a draftsman to spend the greater portion of a week estimating the area coverage of a single average-sized, e.g. 20 inches by 30 inches, sheet having complex artwork thereon. The large number of computations and approximations which must be made in estimating the area of complex artwork tends to make such an estimation process inaccurate because of the high risk of error in making the many computations and because of the inherent inaccuracy in approximating the area of certain irregular shapes using regular figures. When the artwork grades from transparent to opaque, accurate estimates are impossible. Estimation inaccuracies on the order of 20% to 25% are not uncommon. In a large production run, e.g. 1,000,000 packages provided on 20 inch by 30 inch carton blanks, a 20% overestimate of the coverage of a color which covers 80% of the package could result in the overpurchase of approximately 500 gallons of ink at a cost of approximately 2 dollars per gallon, resulting in a total unnecessary cost of approximately $1000 for that color, in addition to the cost involved in preparing the coverage estimate. Thus, it may be seen that a need exists in the packaging arts for an apparatus capable of quickly and accurately measuring the medium coverage of a transparency of the type provided to a package producer by a manufacturer.